(1) Field of the Invention
The present invention relates to the field of rotorcraft having at least one rotary wing rotor. The present invention relates more particularly to data processing methods adapted to a specific function of determining a setpoint for transmission to a regulator unit for regulating the operation of a power plant of the rotorcraft to ensure that it drives said at least one rotor at a given speed of rotation.
Still with reference to the field of the present invention, the function of determining said setpoint takes account more specifically of anticipating power needs that must be delivered by the power plant in order to drive said at least one rotor at a given speed of rotation.
(2) Description of Related Art
In the field of aviation, rotorcraft are rotary wing aircraft provided with at least one rotor. Such a rotor is specifically at least one main rotor having an axis that is substantially vertical and providing the rotorcraft at least with lift. In the context of a helicopter, the main rotor provides the rotorcraft not only with lift, but also with propulsion and/or flight guidance in pitching and in roll.
Rotorcraft are also fitted with an anti-torque device. By way of example, such an anti-torque device is an air propulsion device, and is more commonly in the form of at least one auxiliary rotor having a substantially horizontal axis and providing the rotorcraft with guidance in yaw. By way of example, such an auxiliary rotor is a tail rotor or a propulsive propeller for a high speed rotorcraft with long range.
The lift of the rotorcraft is provided by the main rotor. It is traditional to vary the lift of the rotorcraft by means of a control for varying the collective pitch of the blades making up the rotary wing of the main rotor. Driving rotation of the main rotor is considered as being a priority, given the essential lift-providing function of the rotorcraft.
With a helicopter, the rotorcraft is guided in pitching and in roll by cyclic pitch variation of the blades of the main rotor. The rotorcraft is conventionally guided in yaw by using the anti-torque device, e.g. by varying the collective pitch of the auxiliary rotor(s) of substantially horizontal axis. A rotorcraft may also be guided in full or in part by means of tiltable flaps or other analogous movable control surfaces fitted to a fixed wing of the rotorcraft, such as one or more elevators, and/or one or more fin flaps.
The rotor(s) of a rotorcraft is/are conventionally driven by a common power plant having one or more engine members. The power plant is also used for driving various members and/or pieces of equipment of the rotorcraft that consume mechanical energy.
By way of example, such members and/or pieces of equipment comprise an electrical machine for electrically powering an electricity network on board the rotorcraft, or indeed a reversible electrical machine that is capable, selectively, of delivering mechanical power for driving the rotor(s). Also by way of example, such members and/or pieces of equipment comprise one or more pieces of ancillary equipment, such as for example a heating, ventilation, and/or air conditioning system.
The engine member(s) of the power plant is/are commonly arranged as a turboshaft engine having a free turbine driven in rotation by a gas generator. The free turbine delivers rotary drive to the rotor(s), conventionally via at least one main gearbox interposed between the free turbine and the rotor(s).
Said members and/or pieces of equipment of the rotorcraft that consume mechanical power are also commonly driven from the main gearbox.
The power plant is dimensioned as a function of a predefined nominal speed of rotation for said at least one main rotor. Historically, the speed at which a main rotor is driven in rotation has for many years been established as a constant, or as being marginally variable over a narrow range of speeds. Historically speaking, the lift provided by the main rotor is adjusted solely by a control for varying the collective pitch of the blades. Any other rotors of the rotorcraft, or indeed said members or instruments of the rotorcraft that consume mechanical power, are driven depending on the power available as delivered by the power plant.
The flight commands as issued by the pilot of the rotorcraft are mutually coupled, in order to ensure that the desired variation in the flight of the rotorcraft matches the power being delivered by the power plant as shared between the various rotors, depending on needs. The various commands for varying the pitch of the blades of the various rotors are generated by a pilot of the rotorcraft using flight controls, such as a human pilot using manual control members or an autopilot acting via calculation means.
The power plant is generally fitted with a unit for regulating its operation (e.g. such as a full authority digital engine control (FADEC)). The regulator unit has a setpoint relating to the power needs that the power plant must deliver for driving the main rotor at said nominal speed. This setpoint is delivered by a control unit of the rotorcraft (e.g. such as an automatic flight control system (AFCS)).
More particularly, the control unit generates information relating to a request for power to be delivered by the power plant in order to satisfy the overall power needs of the rotorcraft. In compliance with the priority power needs of the main rotor, the control unit generates a setpoint relating to the power needs of the main rotor driven at a given speed of rotation, and depending on a previously-identified flight state of the rotorcraft. Such a setpoint is calculated by the control unit depending on said given rotary drive speed for the main rotor for a given flight state of the rotorcraft.
Said setpoint is transmitted by the control unit to the regulator unit in order to cause the operation of the power plant to be regulated as a function of the immediate torque needs of the main rotor, and consequently as a function of the immediate torque needs of any other rotors of the rotorcraft, or indeed as a function of power needs of ancillary equipment of the rotorcraft that consumes mechanical energy.
For this purpose, the setpoint is determined in particular by making use of flight controls operated by the pilot, with the power that needs to be delivered by the power plant being deduced from those flight controls. The regulator unit incorporated in the power plant processes the setpoint issued by the control unit in order to determine the quantity of fuel needed by the power plant in order to satisfy the need for driving the main rotor at its nominal speed, given the power needs identified by the setpoint.
On this topic, reference may be made for example to Document U.S. Pat. No. 3,174,284 (United Aircraft Corp.), which describes modes of operating such a regulator unit.
Alternatively, as disclosed by Document U.S. Pat. No. 5,314,147 (United Technologies Corp.), the setpoint is processed by the regulator unit not only depending on the load applied to the rotor(s) as defined by the flight commands issued by the pilot, but also while taking account of a particular flight situation of the rotorcraft, such as a combat situation in which a weapon of the rotorcraft is activated.
Still concerning a particular situation from which the regulator unit defines the quantity of fuel needed by the power plant, reference may be made to Document U.S. Pat. No. 4,466,526 (Chandler Evans Inc.), which describes modes for injecting fuel as a function of the main rotor being put into autorotation.
Regardless of the power that the regulator units may possess, it is nevertheless observed that discrepancies occur between the value of the setpoint issued by the control unit and the speed at which the main rotor is actually driven in rotation. Such discrepancies may result from the structure of the rotorcraft, e.g. because of inertia in the free turbine slowing down its response to being driven by the gas generator, or because of the inertia of the drivetrains for operating the blades or the rotors.
Such inertias have led designers to develop means for enabling the control unit to anticipate the power needs to be delivered by the power plant for driving the rotor(s) at the setpoint speed. The operation of the power plant itself is then governed by the regulator unit on the basis of the setpoint that is transmitted thereto by the control unit in order to obtain actual rotary drive of the main rotor at the setpoint speed while taking account of the flight commands previously issued by the pilot of the rotorcraft.
For example, in the context of electric flight controls, Document US 2008/0283671 (Sikorsky Aircraft Corp.) proposes making use of the signals issued by a pilot in order to generate a power setpoint. More particularly, depending on the flight commands issued by the pilot, the control unit uses anticipation in order to deduce a power setpoint for the power that the power plant is to deliver, and transmits this anticipated power setpoint to the regulator unit. Advantage is taken of the response time of the rotorcraft between issuing flight commands and actual variation in the pitch of the blades of the main rotor in order to generate said power setpoint in anticipation.
Furthermore, changing technology has led rotorcraft designers to envisage modifying the speed of rotation of the main rotor by using a control order that depends on a variation in the values of various parameters.
In particular, it is known voluntarily to cause the value of said setpoint as generated by the control unit to vary over an acceptable range of speeds given that flight conditions of the aircraft must be kept safe. By way of example, variation in the value of the setpoint may be controlled as a function of variation in the flying or “air” speed of the rotorcraft in order to improve its performance. On this topic, reference may be made to the publication “Enhanced energy maneuverability for attack helicopters using continuous variable rotor speed control” (C. G. Schaefer Jr., F. H. Lutze Jr.); 47th Forum American Helicopter Society 1991, pp. 1293-1303.
Proposals have also been made to vary the rotary drive speeds of the main rotor depending on two predefined limiting speeds for an acceptable range of speeds of rotation for the main rotor, providing that flight of the rotorcraft is kept safe.
For example, according to document US 2007/118254 (G. W. Barnes et al.), proposals are made to vary the speed of rotation of the rotor selectively depending on a maximum speed or a minimum speed as a function of the values of parameters relating to the ambient outside medium in which a rotorcraft is operating. By way of example, such parameters are identified from the height of the rotorcraft above the ground, its pressure altitude, its density altitude, or outside temperature.
Also by way of example, document U.S. Pat. No. 6,198,991 (Yamakawa et al.) proposes modifying the speed of rotation of the main rotor when the rotorcraft is in an approach stage coming up to a landing zone, by adapting the path followed by the rotorcraft in order to reduce the sound nuisance it generates.
Nevertheless, it has been found that known rules for anticipating power needs of the power plant are insufficient for such modes of controlled variation in the rotary drive speed of the main rotor.